1. Field of the Invention
The present invention relates to the field of image processing. In particular, the present invention relates to automatically finding transparencies and colors for pixels to mimic de-blending color of a physical medium such as paper and color of a coloring substance such as ink applied thereto.
2. Description of the Related Art
Various devices such as electronic pens, pressure sensitive pads, etc. are available to allow artists to make digital sketches or drawings. However, often, designers or artists prefer to make a sketch or drawing on paper and then scan it into digital form. In digital form, a sketch or drawing may be further refined, or used to assist the designer in the initial stage of building a 3-D model, or used as a texture, and so on. Using a scanned drawing to these ends generally requires an image of the drawing that is transparent where there is no color or ink in the image. To use an image of a sketch or drawing as a layer in another image or in a 3-D model, the artist needs an image that is generally transparent where they have not drawn anything, and that is generally opaque where they have.
Paper has been rendered fully transparent algorithmically by making transparent those pixels of an image that have a color the same as or close to a color of the paper. For example, given a scanned image of a drawing on yellow paper, all pixels close in color distance to the yellow paper color would be made transparent. This approach does not allow pixels to be partially transparent and visual artifacts are common. Where partial transparency has been used, the transparency processing has not been able to preserve hues and saturations of original image colors.
Other techniques for rendering the paper of a scanned drawing transparent have been labor-intensive and have produced unsatisfactory results. In Adobe Photoshop, a magic wand can be used to select regions of a generally uniform color, and a mask tool can be used to mask an image according to a color range. However, these labor-intensive techniques also do not produce images with opacities, hues, or saturations that appear natural or expected.